Trisodium phosphate-sodium nitrate



Patented Dec. 13, 1932 UNITED STATES PATENT OFFICE FBEDERIC CHARLES BOWMAN,

OF LOS ANGELES, CALIFORNIA, ASSIGNOB TO A. R.

MAAS CHEMICAL C0,, OF LOS ANGELES, CALIFORNIA, A CORPORATION OF CALI- FOBNLA TRISODIUM PHOSPHATE-SODIUM NITZRATE No Drawing.

. This invention relates to a trisodium phosphate-sodium nitrate and to the method of preparing compounds of trisodium phosphate and sodium nitrate wherein the sodium nitrate is substituted in the sodium phosphate for sodium hydroxide.

Trisodium phosphate in its commercial form contains free sodium hydroxide and as sold commercially has the exceedingly great disadvantage of caking readily at ordinary summer temperatures. The free sodium hydroxide carried by the commerci l trisodium phosphate also produces a further disadvantage in the production of solutions which are of strongly irritating character due to the presence of the free sodium hydroxide so that strong solutions of the trisodium phosphate containing free sodium hydroxide can not be utilized without considerable irritation to the skin of the hands or other portions of the body contacted by the solution.

In the preparation of a non-caking, nonirritating form of sodium phosphate, I have found that trisodium phosphate, which is generally assigned the chemical formula of as it appears in the commercial salt, contains 2 to 3% excess sodium hydroxide, and that this sodium hydroxide is actually present in the crystalline form of the tr sodium phosphate as substituted in part for one molecule of the twelve molecules of water of crystallization given in the above formula.

I have determined that ordinary trisodium phosphate is a variable solid solution of probably two forms of trisodium phosphate, the variable solid solution of these two forms being apparently a mixture of indicating that all or part of one of the twelve waters of crystallization may be replaced or is replaced by mol. of sodium hydroxide.

I have found that this sodium hydroxide which has apparently replaced a portion of one of the waters of crystallization of the commercial trisodium pho phate may be itself substituted in the crystal form by sodium nitrate so that the resultant compound of tri- Application filed August 24, 1931. Serial K0. 559,138.

sodium phosphate-sodium nitrate does not have the caking properties of the ordinary trisodium phosphate-sodium hydroxide, and does not have the skin irritating properties of the trisodium phosphate containing free sodium hydroxide.

The chemical formula of the trisodium phosphate-sodium nitrate may perhaps be best expressed in the crystal form which it takes when the substitution of sodium nitrate for sodium hydroxide has been carried to its practical limit as 4 (Na PO,.11H O) (NaNO ,NaOH).

I have found that no excess of nitrate, however great, will push the sodium nitrate content of the crystals above 5.6%. The formula 4 (Na PO .11H O)+NaNO has a theoretical sodium nitrate content of 5.55% NaNO indicating that when a large excess of sodium nitrate is utilized, the substitution of sodium nitrate for sodium hydroxide may be carried to completion. and that the sodium nitrate will completely be substituted for the sodium hydroxide present in the ordinary commercial form of trisodium phosphate.

I have found that to carry the sodium nitrate content of the trisodium phosphatesodium nitrate compound to over 4% sodium nitrate requires the use of too great an excess of sodium nitrate in the crystallizing solution in order to be commerc ally feasible, and that when approximately 3% sodium nitrate is substituted into commercial trisodium phosphate for the sodium hydroxide thereof. the resultant compounds, which may be defined as trisodium phosphate-sodium nitrate-sodium hydroxide, plus the water of crystallization. gives to the resultant compound the qualities desired of reducing the irritating property of the ordinary trisodium phosphate. and eliminates to a satisfactory degree the caking property of the trisodium phos ph ate containing all free sodium hydroxide.

In the preparation of the complex salt of trisodium phosphate and sodium nitrate, I have found that the sodium nitrate is substituted for the sodium hydroxide to a practica r at? p extent only when there is employed a comparatively high excess of sodium nitrate in the crystallizing solution formed by the dissolving of sodium nitrate and trisodium phosphate.

I have also found that if the alkalinity of this crystallizing solution is too high, or there is too great an excess of free sodium hydroxide or alkali in the crystallizing solution, that the substitution of sodium nitrate for the sodium hydroxide will not take place to any marked or practical extent.

In considering the alkalinity of the crystallizing solution, it is most convenient to express this alkalinity as alkaline ratio. which is the ratio of titration with phenolphthalein to the further titration with methyl orange. Trisodium phosphate has therefore a ratio or alkaline ratio of 1.

The best ratio or alkaline ratio for the crystallizing liquor I have found is approximately 1. The eiiect of increased alkaline ratio for a given excess of sodium nitrate in a crystallizing liquor is shown by the following table:

Table A Experiment No. 1 2 3 Ratio of rrystallizinc liquor 0.50 1.00 1.49 Ratio of mother liquor 0.39 0. 526 4. 36 Analysis of crystals:

Ratio 1.035 1.072 1.293

NaN 4.00% 4.\% 0.10%

NaOH 0. 22% 0.7% 2. 85%

The low nitrate content of the crystals in Experiment No. 3 was partly due to the fact that only one-half as great an excess of sodium nitrate was present as in the other two experiments. In Experiment No. 1, at the end oicrystallization crwodium phosphate began to be formed.

The effect of the concentration or excess of sodium nitrate in the crystallizing liquor is shown by the following table:

Table B Experiment No. l I 2 1 3 4 5 NaNtuT in liquor 0.05 lens 0.70 1.5 8 2.84 NBN"1IP1 5lD crystals 0.0? 0.04 0.7 0.22 0.31 NaNO; in crystals 0.40% 0.65% 4.00% 4.04% 5.84%

the successive recrystallization five times of a lot of trisodium phosphate-sodium nitrate:

Table 0 Crop No. 1 2 3 4 5 w NaNP; 3.14% 2.60% 1.26 0.42% 0.0? 7 Alkalineratio 1,030 toes 1.132 1.159 1.193

the balance being in each case the water of crystallization.

An analysis of Experiment No. 5, shown in Table B, showed The chemical formula of trisoduim phosphate-sodium nitrate or trisodium phos- -phate-soduim nitrate-sodium hydroxide in crystalline form as shown by this experiment 1s:

4 (Na PO l1H O) (NaNO ,NaOH).

In the preparation of the t-risodium phosphate-sodium nitrate compounds, I have also discovered that not only may complex salt of sodium phosphate-sodium nitrate and sodium hydroxide be formed, but other complex salt may be formed wherein sodium nitrate is partially substituted for the sodium hydroxide contained in the commercial form of trisodium phosphate, for example, mixtures of sodium salts of monobasic acids such as sodium chloride or the like may be substituted with sodium nitrate for a portion of the sodium hydroxide which has apparently displaced one of the waters of crystallization of the commercial form of trisodium phosphate. I have found, for example, that trisodium phosphate-sodium nitrate-sodium chloride-sodium hydroxide may be formed MPOSRTIONS.

mamas having in percent substantially the following composition showing that the salts of the dodecahydrate series form solid solutions with each other freely, and av salts of even greater complexity could be built up if desired.

In carrying out the method embodying my invention for the formation of sodium phosphate-sodium nitrate compounds, I prefer to proceed as follows:

For example. commercial trisodium phosphate is dissolved with sodium nitrate in water, and the composition of the crystallizing liquor is determined. In dissolving the trisodium phosphate and the sodium nitrate in water, heat is applied so that the salts dissolve.

In order to maintain the correct alkalinity ratio of approximately 1, the following illustrative example of an actual production of trisodium phosphate-sodium nitrate is given:

Grains Commercial trisodium phosphate"--- 1200 Commercial 26 Baum disodium phosphate solution 488 Commercial sodium nitrate 154 were dissolved by heating in a large evaporating dish in 1000 grams of water. The composition of the batch was then determined to be Grams per 0. c.

P 0 0 138 NaSO 0.07

from the solution. washed with dilute alcohol.

then with strong alcohol, and finally dried in a thin layer for several hours at approximately 20 C. The crystals produced were fine. glistening hexagonal crystals which, on analysis showed Percent NaRPO, 41.1 NaNO 4.06 Free NaOH 0.9 H 0 by difierence 53.94

In carrying out the process commercially it has been found that the alkalinity of the crystallizing liquor controls the size of the crystals that are formed and that there is UKUDD Kilt LN Llibl;

little latitude in the alkalinity required for the production of marketable crystals. A representative factory run given, for example, is:

Crystallizing liquor Volume 3000 gals. Baum 305 Tem 114 C. Na O, 12.65% Kano. 9.26% NaOH 0.32% Alkaline ratio 1.10

Crystals produced 'Weight 9100 lbs. Na PO, 43.59% NaNO 3.32% NaOH 0.56% Alkaline ratio 1.05

The mother liquor was analyzed and showed the following:

2100 gallons having a specific gravity of 23.50 Bauni at a temperature of 27 C., and containing Na-J O. 6.24% NaNO 10.9% Alkaline ratio 1.07

In crystallizing the crystals from the mother liquor, the crystallizing liquor was placed in a stirred water-cooled crystallizer over night. The crystals were then centri fuged, washed and dried at about 38 C., and barrelled.

Having fully described my invention, it is to be understood that I do notwish to be limited to the details herein set forth, but my invention is of the full scope of the appended claims.

I claim:

1. The herein described composition of matter consisting of a compound of sodium phosphate and sodium nitrate.

2. The herein described composition of matter consisting of a compound of trisodium phosphate and sodium nitrate.

3. The herein described composition of matter consisting of a compound of trisodium phosphate and sodium nitrate in crystalline form.

4. The herein described trisodium phosphate composition containing not less than .08% sodium nitrate.

5. The herein described trisodium phosphate composition containing approximately 08% to 5.55% sodium nitrate.

6. The herein described composition of matterhaving a formula nxa roaungo (NaNO ,NaOH).

7. The herein described composition of matter consisting of a compound of sodium phosphate, sodium nitrate and sodium hydroxide.

Examiner 8. The herein described composition of matter consisting of a compound of sodium phosphate, sodium chloride and sodium nitrate.

9. The herein described alkaline composition of matter which consists of sodium phosphate-sodium nitrate.

10. The herein described composition of matter of crystalline form consisting of 41% to 43.6% trisodium phosphate, 5.55% to .OS% sodium nitrate, and 0.22% to 2.10% sodium hydroxide and water of crystallization.

11. The herein described composition of matter of crystalline form consisting of sodium phosphate, a plurality of salts of monobasic acids, sodum hydroxide and water of crystallization.

12. The herein described process of manufacture of a sodium phosphate-sodium nitrate compound which includes the steps of dissolving sodium phosphate and sodium nitrate in water at an elevated temperature to produce a mother liquor having an alkaline ratio of approximately 1 and crystallizing sodium phosphate sodium nitrate crystals from the mother liquor.

.13. The herein described method of manufacturing sodium phosphate-sodium nitrate compound, which includes the steps of dissolving sodium phosphate and a large excess of sodium nitrate in water at an elevated temperature to produce a mother liquor havfree sodium hydroxide of the sodium phos- FREDERIC CHARLES BOWMAN.

ing an alkaline ratio of approximately 1,

and crystallizing sodium phosphate-sodium nitrate crystals from the mother liquor.

14. The herein described process of manui facturing trisodium phosphate-sodium nitrate compound, which includes the steps of dissolving trisodium phosphate, disodium phosphateimdiniwi l l in water at an elevated temperaturej i'lijd crystallizing sodium phosphate-sodium n1- trate crystals from the mother liquor.

15. The herein described process of manufacture of a sodium phosphate-sodium nitrate compound, which includes the steps of dissolving a sodium phosphate and a plurality of salts of monobasic acids in water, one of which salts of monobasic acids is a sodium nitrate salt, at an elevated temperature to produce a mother liquor having an alkaline ratio of approximately 1, and crystallizing from the mother liquor crystals of salts containing sodium phosphate and the salts of the monobasic acids.

16. The herein described process of manufacture of a sodium phosphate-sodium nitrate compound, which includes the steps of dissolving a sodium phosphate including free sodium hydroxide and sodium nitrate in water at an elevated temperature, and crystallizing from the solution sodium phosphate-s0dium nitrate crystals wherein the sodium nitrate has replaced a portion of the 

